CJ: CJ-7 Quit Runing...Sparks Once But Won't Start

[Racer_X]

Please be kind since this isn't even 'technically' my jeep. The brother-in-law (who now lives in Alaska) left a 85 CJ-7 at our house for transportation and fun when he comes back to California. He was back about two months ago and while his mechanic skills are kind of scary for me (his tool box contains only duct tape and a coat hanger), the jeep was running...until he was driving it down the road and the motor stopped. Checking it and it was getting fuel but removing a plug showed that there was no spark at the plug. After towing it back to the house we started trying to find the problem. When he turns the key from the start position back to run, the jeep seems to fire just once then dies. He does have a parts jeep so we were able to swap out parts to test (I know, never assume that used parts work). We replaced the coil, plugs, wires, cap and rotor with no change. Next was the ignition module and still nothing. Finally, I got out a multimeter and did some checks. The one thing that doesn't make sense and is definitely not right is at the positive wire going into the coil. I know, 8 volts when in run, 12 volts during start...but it actually drops to 5 volts during start. I'm just not sure what needs to be replaced (and he has since gone back to Alaska leaving me a dead jeep in the driveway, but I can use it if I get it fixed...and the woman doesn't have it towed). This is probably something simple that I'm just overlooking but I'm not sure what. Any suggestions?

[6spdYJ]

Try replacing the condenser (the silver can-looking thing under the distributor cap). If these go bad they will only allow one discharge - if that - and then can't keep up to keep the engine running. The condenser is a capacitor. It's basically a storage tank for DC energy. It electrically acts like an accumulator tank on an air compressor. It charges up between cylinders firing and then dumps that power into the coil output for each firing.

The other thing would be to check the positive leg of the coil for continuity back to the alternator and then check the alternator for an internal short.

[aw12345]

Couple of questions straight6? or V8? Stock engine? Stock ignition?
mOST COIL;S GET 12 VOLTS DURING CRANK, WHEN RUNNING OR JUST WITH THE KEY ON AROUND 8-9 VOLTS IS ABOUT NORMAL. Unless it has a HEI distributor. Run a wire from the battery to the positive terminal of the coil, got spark then?

[Racer_X]

Opps, forgot some of the important parts. Straight 6, stock ignition. I ran a wire straight from the battery positive to the positive on the coil and no go. I've also checked out everything in the starter solinoid and it's all good.

BTW, born and raised in Ontario CA. (now living in Nor Cal however).

[aw12345]

So it should use a Ford ignition module and distributor. Does the rotor turn when you crank it?

[aw12345]

So it should use a Ford ignition module and distributor. Does the rotor turn when you crank it?

I scanned this a long time ago, should help you some. Is out of a diagnostic manual.

http://public.fotki.com/aw12345/cj7-ignition/

[Russ Chung]

Jeff,

Here's a link to a PDF version of the service manual; I downloaded it and found it was easier to read than the images of the service manual pages that was linked in Art's post:
http://www.jeep4x4center.com/jeep-se...m=auto,-15,794

1. The troubleshooting chart on page C-62 says that the primary voltage with the key ON should be 5.5v - 6.5v. Since your primary voltage is reading 8 volts, the next step in the troubleshooting chart is to disconnect the wires at the starter solenoid (the power to the coil comes from the starter solenoid and also from the ignition key). If the voltage is 5.5v - 6.5v with the key ON, then the solenoid is bad. If it is still showing 8 volts, then the troubleshooting chart lists three other things to check to determine if the problem is in the wiring or if the ignition control module is bad (but you said that you have already replaced the ignition module)
2. If it still doesn't run, the next test in the troubleshooting chart says to test the coil. Since we know that you get the Jeep to fire once, I'd skip the coil test and go on to the tests of the pickup coil and trigger wheel beginning on page C-66.

Based on the tests that you've already done and the parts that you've already replaced, I suspect that the problem is likely to be the starter solenoid or the pickup coil.

Russ